**8. Biogas production from agro-industrial wastewaters**

#### **8.1 Case vinasses of tequila**

Tequila is a Mexican regional alcoholic beverage obtained from the fermentation of sugars from the cooked stems of blue agave (Agave tequilana Weber var. azul). Its production and

Biogas Production from Anaerobic Treatment of Agro-Industrial Wastewater 107

liter of Tequila produced, 1.4 kg of bagasse and 10–12 L of vinasses are generated. Under this basis of calculation, it is estimated that the production of Tequila in 2010 generated

In the majority of the Tequila factories, bagasse is converted into compost, which is also done in the agave plantations. However, approximately 80% of the vinasses are discharged directly into water bodies (rivers, streams, lakes, reservoirs) and municipal sewer systems or directly onto the soil without receiving adequate treatment for discharge. This common practice causes a deterioration of different degrees to the water bodies receiving the discharges due to low pH, high temperature and elevated concentrations of both BOD and COD of these effluents. On the contrary, if the vinasses receive appropriate treatment and management, they can be used as a source of nutrients and organic matter in agricultural activities; they can also be a potential source of renewable energy. A summary of the physicochemical characteristics of the vinasses generated from the process of producing

**Parameter Value**

262.2 million kilograms of bagasse and 1,873.0 million liters of vinasses.

traditional Tequila (100% agave) is shown in Table 7 (Lopez-Lopez, 2010).

pH 3.4-4.5 Oils and fats (mg/L) 10-100 Total COD (mg/L) 60,000-100,000 Soluble COD (mg/L) 40,000-80,000 Total BOD (mg/L) 35,000-60,000 Soluble BOD (mg/L) 25,000-50,000 Total solids (mg/L) 25,000-50,000 Total suspended solids (mg/L) 2,000-8,000 Fixed suspended solids (mg/L) 10-500 Volatile suspended solids (mg/L) 1,990-7,500 Total dissolved solids (mg/L) 23,000-42,000 Settleable solids (mL/L) 10-900 Total alkalinity (mg/L) < 6.00 Total acidity (mg/L) 1,500-6,000 Fixed acidity (mg/L) 1,480-5,800 Volatile acidity (mg/L) 20-200 Ca (mg/L) 200-1,100 Mg (mg/L) 100-300 K (mg/L) 150-650 Phosphates (mg/L) 100-700 Total nitrogen (mg/L) 20-50 NH4+-nitrogen (mg/L) 15-40 Organic nitrogen (mg/L) 5.0-10 Total reducing sugars (% w) 0.5-2.0 Direct sugars (% w) 0.4-1.0 Cu (mg/L) < 3.0 Fe (mg/L) < 45 Ni (mg/L) < 0.02 Zn (mg/L) < 1.0

Table 7. Physicochemical characteristics of Tequila vinasses (Lopez-Lopez 2010)

commercialization is verified and certified by the Mexican Tequila Regulatory Council (CRT) (NOM-006-SCFI-2005, 2006). In 2008 the CRT registered 139 producers and 1,018 brands of Tequila (bottled in Mexico and in foreign countries, CRT 2008). Based on the number of employees, only 7% are large factories and the rest are small and medium factories, with a grand total of around 30,500 direct employees (National Tequila Industry Chamber, CNIT 2009). Therefore, this industry represents an important economic activity for the 180 Mexican municipalities within the *appellation d'origine contrôlée* granted in 1995 for Tequila.

Tequila production has had an important increase from 2004 to 2008, as it is shown in Fig. 3. In 2010 about 187.3 million liters of Tequila (55% Alc. Vol.) has been produced with a projection for annual growth of at least 10% (CNIT 2010); there is also a decrease in production of Tequila between 2000 and 2003, due to the agave crisis (Dalton 2005). Although exhaustive reviews regarding the treatment of different distillery wastewaters are published elsewhere (Satyawali and Balakrishnan 2008; Mohana et al. 2009), it is considered that special attention should be paid to distillery effluents from the Tequila industry due to their complex composition. This section present the potential generation of energy from wastewater treatments to generate biogas from the Tequila industry.

**Year**

The production of Tequila generates large quantities of bagasse and vinasses. Bagasse is a residual solid; it is generated in the elaboration of Tequila and is produced during the extraction of juice from the cooked heads of agave. Vinasses are the liquid residues that are generated and remain in the bottom of the still after the distillation of the must of fermented agave.

Vinasses are dark brown in color, because they contain phenolics (tannic and humic acids), melanoidins that are low and high molecular weight polymers formed as one of the final products of Maillard reaction (Satyawali and Balakrishnan 2008). It is known that for each

commercialization is verified and certified by the Mexican Tequila Regulatory Council (CRT) (NOM-006-SCFI-2005, 2006). In 2008 the CRT registered 139 producers and 1,018 brands of Tequila (bottled in Mexico and in foreign countries, CRT 2008). Based on the number of employees, only 7% are large factories and the rest are small and medium factories, with a grand total of around 30,500 direct employees (National Tequila Industry Chamber, CNIT 2009). Therefore, this industry represents an important economic activity for the 180 Mexican

Tequila production has had an important increase from 2004 to 2008, as it is shown in Fig. 3. In 2010 about 187.3 million liters of Tequila (55% Alc. Vol.) has been produced with a projection for annual growth of at least 10% (CNIT 2010); there is also a decrease in production of Tequila between 2000 and 2003, due to the agave crisis (Dalton 2005). Although exhaustive reviews regarding the treatment of different distillery wastewaters are published elsewhere (Satyawali and Balakrishnan 2008; Mohana et al. 2009), it is considered that special attention should be paid to distillery effluents from the Tequila industry due to their complex composition. This section present the potential generation of energy from

municipalities within the *appellation d'origine contrôlée* granted in 1995 for Tequila.

wastewater treatments to generate biogas from the Tequila industry.

0

50

100

**Tequila Production (Lx106)**

150

200

250

Fig. 3. Dynamics of Tequila production (55% Alc. Vol.). (calculated from CNIT 2010)

remain in the bottom of the still after the distillation of the must of fermented agave.

The production of Tequila generates large quantities of bagasse and vinasses. Bagasse is a residual solid; it is generated in the elaboration of Tequila and is produced during the extraction of juice from the cooked heads of agave. Vinasses are the liquid residues that are generated and

**Year**

Vinasses are dark brown in color, because they contain phenolics (tannic and humic acids), melanoidins that are low and high molecular weight polymers formed as one of the final products of Maillard reaction (Satyawali and Balakrishnan 2008). It is known that for each liter of Tequila produced, 1.4 kg of bagasse and 10–12 L of vinasses are generated. Under this basis of calculation, it is estimated that the production of Tequila in 2010 generated 262.2 million kilograms of bagasse and 1,873.0 million liters of vinasses.

In the majority of the Tequila factories, bagasse is converted into compost, which is also done in the agave plantations. However, approximately 80% of the vinasses are discharged directly into water bodies (rivers, streams, lakes, reservoirs) and municipal sewer systems or directly onto the soil without receiving adequate treatment for discharge. This common practice causes a deterioration of different degrees to the water bodies receiving the discharges due to low pH, high temperature and elevated concentrations of both BOD and COD of these effluents. On the contrary, if the vinasses receive appropriate treatment and management, they can be used as a source of nutrients and organic matter in agricultural activities; they can also be a potential source of renewable energy. A summary of the physicochemical characteristics of the vinasses generated from the process of producing traditional Tequila (100% agave) is shown in Table 7 (Lopez-Lopez, 2010).


Table 7. Physicochemical characteristics of Tequila vinasses (Lopez-Lopez 2010)

Biogas Production from Anaerobic Treatment of Agro-Industrial Wastewater 109

in the bioreactor depends on the origin of the liquid. In the Table 8, is shows the methane

house CSTR 20-30 0.2-0.3 37 70-80 0.45 [2] \*

vinasses UASB 2.0-2.5 2.0-12.0 37 50-85 0.46 [3] \*

vinasses CSTR 20-30 2.5-12.7 35 50-75 0.42 [4] \*

coffee CSTR 20-30 0.2-0.4 35 60-75 0.37 [5] \*

In all previous cases, the wastewaters are discharged directly into the body of water, causing several environmental pollution in addition to the loss of the energetic potential

Ahn, Y.H., Song, Y.J., Lee, Y.J. and Park, S. (2002). Physicochemical characterization of UASB sludge with different size distributions. *Environ. Technol.* 23, 889–897. Altas, L. (2009). Inhibitory effect of heavy metals on methane-producing anaerobic granular

Cantrell, K.B., Ducey, T., Ro, K.S. and Hunt, P.G. (2008). Livestock waste to bioenergy

Chae, K.J., Jang, A., Yim, S.K. and Kim, I.S. (2007). The effect of digestion temperature and

Choorit, W. and Wisarnwan, P. (2007). Effect of temperature on the anaerobic digestion of

\* [1] López-López, A., Vallejo-Rodríguez, R. and Méndez-Romero, D. C.(2010) Evaluation of a combined anaerobic and aerobic system for the treatment of slaughterhouse wastewater, Environmental

[2] Padilla-Gasca E, López-López A, Gallardo-Valdez J (2011) Evaluation of Stability Factors in the Anaerobic Treatment of slaughterhouse Wastewater. J Bioremed Biodegrad 2:114. doi:10.4172/2155-

[3] López-López A (2011) Evaluación de alternativas de tratamiento para vinazas tequileras, internal

[4] Del Real J., Prieto F., Santos E.M., Román A.D., and Gordillo A.J. (2007). Factibility of treat wineyard wastewater through anaerobic biodigestion with from cow's waste. Rev. Téc. Ing. Univ. Zulia. Vol. 30

[5] Del Real Olvera J. and Islas Gutiérrez J. (2010). Anaerobic biodegradation of wastewater produced in

temperature shock on the biogas yields from the mesophilic anaerobic digestion of

**Temperature (°C)** 

filter 0.6-3.0 3.7 -16.5 25 50-81 0.41 [1] \*

**COD removed (%)** 

**MPR (m3CH4/kg COD)** 

**Ref.** 

**OLR (kg COD/m3-d)**

production rate from wastewater of different types.

**HRT (days)** 

Table 8. Methane production rate from wastewater of different type\*

sludge. *J. Hazard. Mater.* 162, 1551-1556.

swine manure. *Bioresour. Technol.* 99(I), 1–6.

project CIATEJ-IVINAZAS2/09/PT. (unpublished data)

coffee pulping. Revista Colombiana de Biotecnología. Vol. 12 (2), 230-239.

generation opportunities. *Biores.Technol*. 99:7941–7953.

palm oil mill effluent. *Electron. J . Biotechnol.* 10(3), 376–385.

**Reactor Type** 

Anaerobic

**Wastewater type** 

Slaughterhouse

Slaughter-

Tequila

Cane

Pulping

contained in the effluents.

Technology, 31: 3, 319 — 326.

6199.1000114.

(2), 128 – 135.

**9. References** 

The anaerobic biological process has been utilized for treating Tequila vinasses on laboratory, pilot and industrial scales due to technical and economical advantages over aerobic processes (Linerio and Guzman 2004; Mendez, et al. 2009). On a laboratory scale, Lopez-Lopez and coworkers (2011), Mendez and coworkers (2009) showed an anaerobic digester capable of removing 90–95% of organic material as COD; generating significant amounts of biogas rich in methane. The most common system found at an industrial level in treating Tequila vinasses is of anaerobic type. Fig.4 shows the amount of energy that can be generated if the entire volume of vinasses is treated.

Fig. 4. Production of biogas from Tequila vinasses as a source of energy
